An embodiment of a lighting device of the kind set forth is known from U.S.2010/0103678. That document discloses an LED component comprising a submount for holding an array of LED chips, with the submount having die pads and conductive traces on its top surface. The LED chips forming the array are mounted to a respective one of the die pads. The conductive traces are arranged to provide electrical power to the LED chips, such that in operation they emit light useable to provide an application specific illumination distribution. The LED component further comprises a solid lens covering the array of LED chips and a diffuser for mixing the light emission of the LEDs in the near field. In other words, the diffuser mixes the emission of the LED chips in an attempt to make, when the LED component is observed, the light originating from the discrete LED chips not as clearly individually identifiable as without diffuser. Instead, when the LED component is viewed directly, it approximates a single light source under the lens. The diffuser could be provided as a dome over the lens, wherein the dome may comprise diffusing microstructures such as scattering centers or micro-lenses.
The advantage of this approach lies in the fact that optical inhomogeneities in the far field are prevented. Such inhomogeneities originate from the discrete geometrical locations on the submount of the LED chips in combination with secondary optics usually employed in luminaires, as for instance a reflector in the case of a spot-light illumination application. As a consequence, shadow lines in the far field illumination pattern would occur in the centre of the illumination distribution and especially in its periphery, if not counter acted. Many lighting designers and users consider such effects annoying. Especially when the LED chips emit light of different colors, these shadow lines are colored. The coloration makes them even more observable and thus more annoying than the lighter/darker modulations in the illumination distribution in case all LED chips emit the same color light.
A drawback of the solution described in U.S.2010/0103678, however, is that it enlarges the size of the light source, both mechanically and optically. The mechanical enlargement is due to the physical size of the dome encompassing the LED chip array. The optical enlargement is due to the spreading of the light emitted by the individual LED chips. While this results in a virtual size of the LED chips in the middle of the array that fills the ‘dark gaps’ between the discrete LED chips, the virtual size of the LED chips near the outer edge of the array extend the size of the light source beyond the physical size of the array. As is well known, a larger light source size complicates the use and design of secondary optics for obtaining an application specific illumination distribution. Especially for narrow-beam spot-light applications, a small light source is desired to maintain a practical and usable size of the secondary optics.